Hasselblad Polarizer Filter - Silly Question

[db1]

I just purchased a Hasselblad Polarizing Filter.

 

Why does it spin, if it's a linear filter?

[jayaprakash_kotha]

Whether linear or circular they both spin to polarize the light. By spinning the filter, your are allowing light polarized in one particular plane into the camera. Thus polarization cuts off some light and you need to compensate for this in making an exposure. THe amount of compensation is usually printed on the filter (at least for hasselblad filters). Linear polarizer will also fool the camera's autofocus system.

A circular polarizer is a linear polarizer with additional mechanism to further process light entering the camera so that autofocus system of the camera works normally.

[ilkka]

Put the filter in front of your eye, look at the world around you and spin the filter. It tells you more about polarising filters than any lengthy explanations.